It is desired to acquire a high degree of capacity in wireless communication networks. One technique to increase capacity in a wireless communication network is to deploy low power pico radio base stations within macro cell coverage areas forming a heterogeneous network. Pico base stations are smaller than regular macro base stations, and cover smaller areas, and are in many cases placed close to street level and a backhaul aggregation point is usually placed at macro base stations above rooftop level.
Traditional wireless backhaul technologies for establishing a connection between pico base stations and a backhaul aggregation point are line-of-sight radio links. However, when the backhaul aggregation points are placed above rooftop level while the pico base stations are below the roof, closer to the street level, line-of-sight (LOS) may be prevented such that a none line-of-sight (NLOS) scenario exists. NLOS propagation scenarios make use of diffraction, reflection, and penetration effects.
At a NLOS propagation scenario, one cannot align the radio link backhaul antenna beams at the macro base station and the radio link backhaul antenna beam at the pico base station towards each other by means of visual inspection and manual adjustment. Traditionally, backhaul connection has then been solved by using for example copper wires or optical fiber wires.
However, the traditional backhaul technologies discussed above do not always fit a heterogeneous backhaul scenario. Wireless NLOS backhaul radio links equipped with high gain antennas have then been proposed as an alternative.
High gain radio link antennas with narrow beams are usually used in LOS applications, having a very narrow beam-width of a few degrees. The alignment process is then very sensitive to pointing errors. Thus, it becomes very hard to align two narrow beam-width antennas towards a common diffraction, reflection or penetration point in an NLOS scenario when there is no visual connection between them.
Aligning antennas in LOS scenarios is described in prior art, for example in WO 2008/047342, US 2010/0302101 and U.S. Pat. No. 6,836,675.
US 2010/0302101 teaches a method of automatic alignment of a first directional beam antenna with a second directional beam antenna at a predetermined path attenuation.
U.S. Pat. No. 6,836,675 teaches a method of achieving best wireless link status of microwave communication system by aiming the antennas at the best direction.
However, none of these documents discloses how to simultaneously align two narrow beam radio link antennas in an NLOS scenario, and there is thus a need for such a method.